Hi - this is my first post here - I'm just trying to understand how moisturizers work.

As best I can tell, moisturizers have 2 most important parts: a humectant and a barrier (occlusive). Usually the humectant is glycerin and the barrier is petrolatum or mineral oil.

(yes, I realize there are more ingrediants like emolliants, but these seem to be the big 2)

If I understand correctly, most of the time humectants draw moisture to the epidermis from the dermal layers underneath, rarely from the external atmosphere, correct? (unless if it happens to be a very humid environment)

And the point of having a barrier-occlusive on top of the humectant is to keep the moisture from escaping (correct, so far?)

My main question: So if we have a barrier on top of the humectant - then there's no way that the humectant could get moisture from the outside atmosphere anyway, right? (because there's a barrier on top of it)

But here's a complex second question: in a perfect world, the barrier would be layered on top of the humectant. But that's not what's really happening - the two substances are mixed together in the moisturizer cream. So doesn't this mean that the occlusive could be preventing the humectant from attracting moisture from both above and below because both substances are blended together?

Applying a serum humectant to a damp face (either water or sprayed hydrosol) and then applying an occlusive cream would solve that issue. You will see this is often recommended as the way to apply your products.

Those two ingredients are the big two primarily because they are cheap as chips, and secondarily because they don't cause negative reactions in the vast majority of people. For optimum results you would choose ingredients that are active rather than inert - not petrolatum nor glycerin.

It is not as simple as that because some humectants/ emollients/ occlusives don't penetrate the skin at all and some do, some combinations assist absorption. Also the barrier dilutes the humectant and vice vera; if you apply a humectant alone many people find it draws water out of the skin and it ends up feeling dry and/ or tight and/ or sticky. It's also not easy to spread a neat emollient/ occlusive, you tend to end up dragging on the skin or with an unpleasantly thick layer.

If you have a good quality aloe vera gel and a light natural oil at home try this: firstly layer one on top of the other, leaving time for the aloe to penetrate and the surface be dry. Another time blend the two together in your palm and then apply.

1. apply the humectant
2. let it dry
3. apply the barrier on top of it

(which implies that the humectant will be drawing water from within)

But does this mean that moisturizers which blend the humectant and barrier are somewhat self-defeating?

Apply humectant (I assume it has actives) to a damp face them follow what you posted above.

On your second question I deffer to an expert:

Moisturizers: What They Are - Practical Approach to Selection: How Do Moisturizers Work?
Authors and Disclosures
Print This

Abstract and Introduction
What Are Moisturizers?
How Do Moisturizers Work?
Emollients
Occlusives
Humectants
Where Are They Used?
What is the Ideal Moisturizer?
Formulation Characteristics
Conclusion
References
Read this article on Medscape's
free mobile app. Download Now
How Do Moisturizers Work?

For many years, epidermal water content has been known to be crucial for skin plasticity and the prevention of "dry skin".[4] Traditionally, moisturization was believed to inhibit transepidermal water loss (TEWL) by occlusion. Water originates in the deeper epidermal layers and moves upward to hydrate cells in the stratum corneum (SC), eventually being lost to evaporation.

The SC architecture is the most important factor in water flux and retention in the skin, and in overall level of moisturization.[5] The four key processes for the formation and functioning of the SC are the corneocyte process, SC lipid process, natural moisturizing factor (NMF) process, and desquamation process.[6] Corneocytes are the physical barrier of the SC and, when hydrated, contribute to elasticity. The lipid bilayers of the SC function as a moisture barrier and although they prevent the entry of many chemicals, they are the means of entry for most topically applied substances. The NMF is found within corneocytes and is a mix of hygroscopic molecules that, by helping maintain hydration in the corneocyte, keep the SC hydrated. Half of the NMF is amino acids derived from the protein filaggrin in keratinocytes, and the other half is salts, including lactates, urea, and electrolytes. Production of NMF is directly related to external humidity. In desquamation, corneodesmosomes are degraded by water-dependent hydrolytic agents. When there is low moisture in the SC, these enzymes do not work efficiently. Corneocytes accumulate on the skin surface producing the signs of dry skin, e.g., when the moisture content is less than 10%, and when there is loss of continuity of the SC.[2]

The moisturizing treatment involves repairing the skin barrier, retaining/increasing water content, reducing TEWL, restoring the lipid barriers' ability to attract, hold and redistribute water, and maintaining skin integrity and appearance. Moisturizers perform these functions by acting as humectants, emollients, and occlusives.[7] Moisturizers containing collagen and other proteins, i.e., keratin and elastin, claim to rejuvenate the skin by replenishing its essential proteins but whether or not they have any effect on skin hydration is questionable.[2] Moisturizers also act to reduce skin friction and increase skin hydration by providing water directly to the skin from their water phase and by increasing occlusion, as measured as a decrease in TEWL.[8] Loden suggests that skin care products not only form an inert, epicutaneous layer, but that they also penetrate and influence the structure and function of the skin.[9]

Moisturizers have little effect on the mechanical properties (i.e., distensibility, hysteresis, and elasticity) of the skin but do increase skin hydration significantly, as shown by an increased skin capacitance.[10] When moisturizers are used to improve skin plasticity it is suggested that lipid-rich formulations be used.[11]

Thanks Darkmoon, I had already seen that article. An earlier section of it (on the Medscape website)claims that "moisturizer" is really just a marketing term with no scientific meaning.

Does anyone agree or disagree? This is what really got me thinking about the claims of "drawing moisture from the atmosphere" - which most of the time it seems they don't.

Likewise, I'm skeptical of why they would mix humectant and barrier if it's self defeating.

I will say that is why I am inclined to make my own serums and oil blends for most uses, I do layer the oil blend at night over my serums, but morning I just use my sunscreen over my serums. I am not all that fond of creams personally.

1. apply the humectant
2. let it dry
3. apply the barrier on top of it

(which implies that the humectant will be drawing water from within)

But does this mean that moisturizers which blend the humectant and barrier are somewhat self-defeating?

I must learn not to write walls of text! No because moisturisers are formulated with percentages that take the mutual dilution into consideration; plus our skin barrier is composed of both humectants and emollients/ occlusives and so is the combination of sebum and sweat it expects to receive as a natural 'moisturiser'. As I said

"It is not as simple as that because some humectants/ emollients/ occlusives don't penetrate the skin at all and some do, some combinations assist absorption. Also the barrier dilutes the humectant and vice vera; if you apply a humectant alone many people find it draws water out of the skin and it ends up feeling dry and/ or tight and/ or sticky. It's also not easy to spread a neat emollient/ occlusive, you tend to end up dragging on the skin or with an unpleasantly thick layer."

No because moisturisers are formulated with percentages that take the mutual dilution into consideration;

OK, so compared to a 2 part routine (apply humectant, let dry, apply occlusive) -in an all-in-one moisturizer product they'll adjust the % of humectant upward to offset the blended-in occlusive that negates it? (occlusive negates the humectant, that is)

Sort of, so that you get the right 'dose' of each component in a product that feels right to apply, not too greasy and not too sticky, and is also effective. Every active has a recommended use rate, a percentage at which it works in a formulation, is effective but still feels right. They won't negate each other any more than salt negates pepper in your meal, you couldn't possibly eat a meal where either one was at high concentration, so they sit happily together each doing their own thing.

If you apply a humectant straight up or in a high concentration it will likely be sticky or feel tight - think of aloe vera gel or honey. So you have to go down to 5% or 50% depending on the ingredient (FYI glycerin is ~5%), but we will say 10% for this example. So if you wanted to apply that separately to your oil you are going to have to use plenty of water, which means your humectant will be runny. So then you need a thickener and a preservative ....

Then your occlusive/ emollient. You certainly can apply an oil straight up but a lot of people don't want to wait for it to absorb or live with a film, they want to leave the house or apply make up. So again you would usually dilute that with water, say 50% for this example (FYI petrolatum would be much lower). Which means you need an emulsifier (oil and water don't mix) and another preservative. PITA right? Or you could just make one cream with 10% humectant, 50% oil, 10% emulsifiers and preservatives and thickeners, 30% water. The only difference is you took some of the water out, you are still applying the same percentages of product, and it's easier to apply a larger 'dose' because there is less water to deal with. Cosmetic scientists know what percentages are effective for a given ingredient because a lot of independent research has been carried out over the years.

On top of that some humectants help some fatty acids/ lipids absorb and vice versa. The top layer of skin used to be thought of as the dead horny layer, but we are learning how active it is. It evolved to be a barrier to water loss to bacteria or chemicals getting in, but we want to persuade it to absorb certain drugs or actives. A high tech example is liposomes, which are fatty shells with an ingredient or drug inside. Because the lipids are similar to the skin we can persuade it to absorb molecules that would normally be too large to cross the skin barrier! Both urea and aloe vera are humectants and research suggests they can be used as a vehicle to help carry other substances inside. Urea can also assist with exfoliation, and aloe has anti-ageing properties.

Sooooo I try not to use or recommend moisturisers that are simply based on glycerin and petrolatum too often, not because they are 'bad' but because we are missing a trick by doing that. There are numerous other ingredients that can hydrate the skin AND work on another of your skincare goals simultaneously. Cosmetic Science is an interesting field IMO, but you will become mired in cell biology and biochemistry if you are not careful! This is an excellent review article on the stratus corneum - written by the late 'godfather' of Retin-A, Albert Kligman - if you are interested
http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2011.00644.x/full

Thanks Firefox, great info! When you mention "actives" are you talking about this list?

Edit: because I'm a new member I can't post a link, even though it's to a page within this website. At the top it says "Active Ingredients in skin care cosmetics"

And if you could pick from that list one humectant and one occlusive (to use in a two-part routine) which would they be?

(and should the humectant "hyluronic acid" be on that list?)

Who was the OP of that thread, Active Ingredients in skin care cosmetics?

It would make it easier to find through search and provide a link.

_________________I'LL SEE YOU ON THE DARKSIDE OF THE MOON....

AzeiteNew Member

Joined: 21 Apr 2012
Posts: 8

Sun Apr 22, 2012 6:44 am

Let me try this:

essentialdayspaDOTcom/ingredients-cosmetics-c_23DOThtm

SystemAutomatic Message

Mon Nov 19, 2018 3:51 pm

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